This trial is conducted in Asia, Europe and North America. The aim of the trial is to compare the effect of semaglutide s.c. 1.0 mg once-weekly versus placebo as add-on to sodium glucose co-transporter-2 inhibitor (SGLT-2i) monotherapy or in combination with either metformin or sulfonylurea on glycaemic control after 30 weeks of treatment in subjects with type 2 diabetes. Subjects will remain on their pre-trial medication.